I can't take quests from npcs such as Wilson and the human in Sewer Town. What about it? Do I need to be of a certain alignement / faction or whatever?

Some quests are turned off, and some quests have restrictions that you won't be told in the description/conversation. So, yes.

I would like to add that the dwarf by the spellguard tower (kronus or something), also lists a quest, but he never talks about it.

Krovus should have in his description information stating that his quest is disabled.

I'd just like to offer this, but if some of your quests are non-operable because you need someone to script or build something, I'm happy to help.